| endogenous reproductive rhythms in a tropical bird. | like other tropical birds, african stonechats breeding at the equator reproduce once a year during the main rainy season and subsequently carry out a complete molt. these two activities are controlled by endogenous circannual mechanisms: in stonechats held in constant conditions of photoperiod and temperature, a rhythm of gonadal size and molt persisted for up to 7.5 years, which would be a lifetime for free-living conspecifics. the fact that the period of these rhythms deviated from 12 months d ... | 1990 | 17773105 |
| daytime light intensity affects seasonal timing via changes in the nocturnal melatonin levels. | daytime light intensity can affect the photoperiodic regulation of the reproductive cycle in birds. the actual way by which light intensity information is transduced is, however, unknown. we postulate that transduction of the light intensity information is mediated by changes in the pattern of melatonin secretion. this study, therefore, investigated the effects of high and low daytime light intensities on the daily melatonin rhythm of afro-tropical stonechats (saxicola torquata axillaris) in whi ... | 2007 | 17406847 |
| testosterone, territorial response, and song in seasonally breeding tropical and temperate stonechats. | testosterone facilitates physiological, morphological, and behavioral changes required for breeding in male vertebrates. however, testosterone concentrations and the link between its seasonal changes and those in reproductive behaviors vary greatly among species. to better understand the impact of tropical and temperate environments and life history factors on this variation, we have compared testosterone, territorial behavior and song performance across sequential stages of the breeding season ... | 2017 | 28412929 |
| migratory restlessness in an equatorial nonmigratory bird. | the urge of captive birds to migrate manifests itself in seasonally occurring restlessness, termed "zugunruhe." key insights into migration and an endogenous basis of behavior are based on zugunruhe of migrants but have scarcely been tested in nonmigratory birds. we recorded zugunruhe of african stonechats, small passerine birds that defend year-round territories and have diverged from northern migrants at least 1 million years ago. we demonstrate that zugunruhe is a regular feature of their end ... | 2006 | 16555925 |
| baseline and stress-induced levels of corticosterone in male and female afrotropical and european temperate stonechats during breeding. | latitudinal variation in avian life histories falls along a slow-fast pace of life continuum: tropical species produce small clutches, but have a high survival probability, while in temperate species the opposite pattern is found. this study investigated whether differential investment into reproduction and survival of tropical and temperate species is paralleled by differences in the secretion of the vertebrate hormone corticosterone (cort). depending on circulating concentrations, cort can bot ... | 2017 | 28532466 |
| endogenous gonadal, lh and molt rhythms in tropical stonechats: effect of pair bond on period, amplitude, and pattern of circannual cycles. | to investigate the effects of reproduction and associated stimuli on the circannual cycles of african stonechats saxicola torquata axillaris birds were held for 29 months in aviaries under a constant equatorial (12.25 h) photoperiod, either singly (10 females and 10 males) or in 10 male/female pairs. the birds of all 3 groups went through circannual cycles in gonadal size, plasma lh and molt, but groups differed with regard to actual reproductive performance. during the second cycle, only one of ... | 1995 | 7623296 |
| is food availability a circannual zeitgeber in tropical birds? a field experiment on stonechats in tropical africa. | equatorial stonechats (saxicola torquata axillaris) in africa are seasonal breeders like their temperate-zone conspecifics (s.t. rubicola). their annual cycle in gonadal size and function is controlled by an endogenous circannual rhythmicity that has been shown to run for up to 10 years in a constant equatorial photoperiod under laboratory conditions, with a period deviating from 12 months. in nature, however, this rhythm is synchronized with the actual year. because photoperiod is essentially c ... | 2002 | 12002164 |
| a tropical bird can use the equatorial change in sunrise and sunset times to synchronize its circannual clock. | at higher latitudes, most organisms use the periodic changes in day length to time their annual life cycle. at the equator, changes in day length are minimal, and it is unknown which cues organisms use to synchronize their underlying circannual rhythms to environmental conditions. here, we demonstrate that the african stonechat (saxicola torquatus axillaris)-an equatorial songbird-can use subtle solar cues for the annual timing of postnuptial moult, a reliable marker of the circannual cycle. we ... | 2012 | 22648153 |
| postjuvenile molt in east african and central european stonechats (saxicola torquata axillaris, s.t. rubicula) and its modification by photoperiod. | twenty-eight stonechats of the european race (saxicola torquata rubicula) from austria and thirty-one stonechats of the central african race (s.t. axillaris) from equatorial kenya were handraised and subsequently investigated with regard to the temporal pattern of their postjuvenile molt. about one half of the birds of each race were held under their own native photoperiod and the other half under the photoperiodic conditions of the other race. the results demonstrated clear differences in the p ... | 1983 | 28310535 |
| moult and basal metabolic costs in males of two subspecies of stonechats: the european saxicola torquata rubicula and the east african s. t. axillaris. | the circannual patterns in resting metabolic rate (rmr) of males of two subspecies of stonechats, the european saxicola torquata rubicula and the east african s. t. axillaris, are compared. as the birds from the two subspecies were raised and kept under comparable laboratory conditions, differences in metabolic rate between the two subspecies had to be genetically determined. rmr peaked during moult in both subspecies. during the rest of the year rmr was fairly constant in both subspecies and as ... | 1995 | 28307657 |
| flexible seasonal timing and migratory behavior: results from stonechat breeding programs. | rigid schedules of long-distance migrants could be among candidate traits for adaptive migratory syndromes. this prediction was tested on stonechats, passerines that differ widely in migratory behavior and seasonal schedules. stonechats in europe are short-distance migrants and multiclutched, whereas african residents and siberian long-distance migrants usually raise single broods. in captivity, all subspecies displayed endogenous cycles of reproductive development and molt. the subspecies diffe ... | 2005 | 16055855 |
| testosterone and corticosterone during the breeding cycle of equatorial and european stonechats (saxicola torquata axillaris and s. t. rubicola). | northern-temperate male birds show seasonal changes in testosterone concentrations with a peak during the breeding season. many tropical birds express much lower concentrations of testosterone with slight elevations during breeding. here we describe testosterone and corticosterone concentrations of male stonechats from equatorial kenya during different substages of breeding and molt. this tropical species has a short breeding season of approximately 3 months. we compare their hormone concentrati ... | 2006 | 16934809 |
| predators as stressors? physiological and reproductive consequences of predation risk in tropical stonechats (saxicola torquata axillaris). | tropical birds usually lay smaller clutches and are less likely to initiate a second brood than their temperate-zone relatives. this reduction in annual fecundity is generally explained as an adaptation either to higher rates of nest predation or to a more limited food supply concurrent with higher adult survival in the tropics. however, the physiological parameters associated with lower annual fecundity in tropical birds have not been well investigated. we compared the annual fecundity, behavio ... | 2001 | 11487404 |